Google’s co-founder Sergey Brin unleashed perhaps the most stinging criticism of the controversial Stop Online Piracy Act that is working its way through Congress.

In a Google+ post, Brin said if the U.S. passed either SOPA, the House version of the bill, or the Protect IP Act, the Senate version, it would put the country in same league as China and Iran as far as Internet censorship is concerned. Brin said the bills were a “threat to free speech.”

Brin writes:

“Two bills currently making their way through congress — SOPA and PIPA — give the US government and copyright holders extraordinary powers including the ability to hijack DNS and censor search results (and this is even without so much as a proper court trial). While I support their goal of reducing copyright infringement (which I don’t believe these acts would accomplish), I am shocked that our lawmakers would contemplate such measures that would put us on a par with the most oppressive nations in the world.”

As we’ve reported, the Motion Picture Association of America, Recording Industry Association of America and the U.S. Chamber of Commerce are behind the legislation, which would create an Internet blacklist and they say control piracy.

Today, a group of technology A-listers, including Brin, sent an open letter to Washington stating why they oppose to the bill. The first one listed is the legislation’s mandate that web services monitor “what users link to, or upload.”

“This would have a chilling effect on innovation,” the letter reads.

The Internet moguls also say the legislation would change the “basic structure of the Internet,” and “deny website owners the right to due process of law.”

The letter is signed by some of the founders of eBay, Craigslist, Paypal, Twitter, Yahoo!, Wikipedia, Flickr, Mozilla, YouTube and others.